Oxide films containing titanium

ABSTRACT

Atomic layer deposition (ALD) type processes for producing titanium containing oxide thin films comprise feeding into a reaction space vapour phase pulses of titanium alkoxide as a titanium source material and at least one oxygen source material, such as ozone, capable of forming an oxide with the titanium source material. In preferred embodiments the titanium alkoxide is titanium methoxide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority as a continuation in part of U.S.application Ser. No. 09/787,062, filed Jun. 28, 2001. The priorityapplication is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to processes for depositingtitanium-containing oxide films. Certain embodiments relate to processesfor manufacturing titanium-containing oxide thin films by atomic layerdeposition using volatile titanium compounds as source materials.

2. Description of the Related Art

Atomic layer deposition (“ALD”) refers to vapour deposition-type methodsin which a material, typically a thin film, is deposited on a substratefrom vapour phase reactants. It is based on sequential self-saturatingsurface reactions. ALD is described in detail in U.S. Pat. Nos.4,058,430 and 5,711,811, incorporated herein by reference. ALD reactorsbenefit from the use of inert carrier and purging gases, which makes thesystem fast.

According to the principles of ALD, the reactants (also referred to as“source chemicals” or “precursors”) are separated from each other,typically by inert gas, to prevent gas-phase reactions and to enable theabove-mentioned self-saturating surface reactions. Surplus chemicals andreaction by-products are removed from the reaction chamber by purgingwith an inert gas and/or evacuating the chamber before the next reactivechemical pulse is introduced. Undesired gaseous molecules can beeffectively expelled from the reaction chamber by keeping the gas flowspeeds high with the help of an inert purging gas. The purging gaspushes the extra molecules towards the vacuum pump used for maintaininga suitable pressure in the reaction chamber. ALD provides controlledfilm growth as well as outstanding conformality.

Titanium containing oxides are technologically very important and theyhave a variety of industrially useful properties. They function well,for example, as semiconductors, insulators and ferroelectrics. TiO₂ hasa high permittivity of around 70. BaTiO₃ and SrTiO₃ have permittivitiesof several hundreds. Titanium also has several technologically importantternary compounds, such as BiTiO₃ and PbTiO₃. Pure TiO₂ is usuallyoxygen deficient and thus semiconducting. Semiconducting TiO₂ has beenused, for example, in solar cells and self-cleaning coatings.

Alkaline earth metals (such as Ba and Sr) easily form stablenon-volatile halides. Therefore, halide-containing precursors of thesemetals are not generally useful in depositing oxides such as SrTiO₃ andBaTiO₃ by ALD. In addition, alkaline earth metals easily formhydroxides. As a result, ALD using water as an oxygen source can beproblematic, requiring long purge times and/or high temperatures.However, long purge times effectively impair the productivity of theseprocesses. Further, it can be difficult to find a deposition temperaturethat will not cause decomposition of the precursors and will keep thethin film atoms intact, but will still keep the precursors in gaseousphase and provide the activation energy for the surface reactions.

SUMMARY OF THE INVENTION

In one aspect atomic layer deposition processes for producingtitanium-containing oxide thin films are provided. The processespreferably comprise alternately contacting a substrate in a reactionspace with vapor phase pulses of a titanium alkoxide reactant, such as atitanium methoxide compound and at least one oxygen source materialcapable of forming an oxide with the titanium. In some embodiments, thetitanium methoxide is Ti(OMe)₄. Preferably, the oxygen source materialis ozone. However, in some embodiments the oxygen source material isselected from the group consisting of water, oxygen, hydrogen peroxide,aqueous solutions of hydrogen peroxide, ozone, oxides of nitrogen,halide-oxygen compounds, peracids (—O—O—H), alcohols, alkoxides,oxygen-containing radicals and mixtures thereof.

In some embodiments, ternary and other multicomponent oxide films aredeposited by providing a second metal source material, preferablycomprising at least one transition metal or main group metal, followedby provision of an oxygen source material.

In some embodiments, the deposition temperature is preferably betweenabout 100° C. and about 300° C.

In another aspect, multicomponent oxide thin films comprising titaniumare deposited by atomic layer deposition type processes. The processespreferably comprise contacting a substrate with alternate and sequentialvapour phase pulses of a metal precursor and an oxygen source material,where the metal precursor is preferably a titanium alkoxide compound andthe oxygen source material is preferably ozone. The titanium alkoxidecompound may be, for example, a titanium methoxide compound. In someembodiments the multicomponent oxide film comprises titanium, barium andstrontium.

In a further aspect, methods are provided for depositing amulticomponent oxide film comprising barium and strontium by repeating afirst, second and third growth cycle. The first growth cycle preferablycomprises contacting a substrate in a reaction chamber with a titaniummethoxide compound, removing excess titanium methoxide, contacting thesubstrate with ozone and removing excess ozone from the reactionchamber. In the second and third deposition cycles, the substrate isalternately contacted with a barium or strontium compound, respectively,and an oxygen source material, such as ozone. The cycles may be repeatedin equivalent numbers. In other embodiments, the ratio of cycles isvaried to achieve the desired film composition, as will be apparent tothe skilled artisan.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a-g are graphical presentations of the range, uniformity andgrowth rate of titanium oxide films deposited at temperatures of100-300° C. using titanium alkoxides as the titanium source material andwater (FIGS. 1 a-1 c) or ozone (FIGS. 1 d-1 g) as the oxidant.Deposition was carried out at 200° C. in FIG. 1 a, at 250° C. in FIG. 1b, at 300° C. in FIG. 1 c, at 150° C. in FIG. 1 d, at 200° C. in FIG. 1e, at 250° C. in FIG. 1 f and at 300° C. in FIG. 1 g.

FIG. 2 is a graphical presentation of the growth rate as a function ofthe growth temperature (deposition temperature). The titanium sourcechemical was Ti(OMe)₄ and the oxidant was ozone. A 200 mm wafer wasmeasured at 49 points.

FIG. 3 is a graphical presentation of the film nonuniformity as afunction of growth temperature. The titanium source was Ti(OMe)₄ and theoxidant wa ozone. A 200 mm wafer was measured at 49 points.

DETAILED DESCRIPTION

In context of the present invention, “an ALD type process” generallyrefers to a process for depositing thin films on a substrate molecularlayer by molecular layer. This controlled deposition is made possible byself-saturating chemical reactions on the substrate surface. Gaseousreactants are conducted alternately and sequentially into a reactionchamber and contacted with a substrate located in the chamber to providea surface reaction. Typically, a pulse of a first reactant is providedto the reaction chamber where it chemisorbs to the substrate surface ina self-limiting manner. Excess first reactant is then removed and apulse of a second reactant is provided to the reaction chamber. Thesecond reactant reacts with the adsorbed first reactant, also in aself-limiting manner. Excess second reactant and reaction by-products,if any, are removed from the reaction chamber. Additional reactants maybe supplied in each ALD cycle, depending on the composition of the thinfilm being deposited.

pressure and the temperature of the reaction chamber are adjusted to arange where physisorption (i.e. condensation of gases) and thermaldecomposition of the precursors are avoided. Consequently, only up toone monolayer (i.e. an atomic layer or a molecular layer) of material isdeposited at a time during each pulsing cycle. The actual

rate of the thin film, which is typically presented as Å/pulsing cycle,depends, for example, on the number of available reactive surface siteson the surface and bulkiness of the reactant molecules.

Gas phase reactions between precursors and any undesired reactions withby-products are preferably inhibited or prevented. Reactant pulses areseparated from each other and the reaction chamber is purged with theaid of an inactive gas (e.g. nitrogen or

and/or evacuated between reactant pulses to remove surplus gaseousreactants and reaction by-products from the chamber. The principles ofALD type processes have been presented by the inventor of the ALDtechnology, Dr T. Suntola, e.g. in the Handbook of Crystal Growth 3,Thin Films and Epitaxy, Part B: Growth Mechanisms and Dynamics, Chapter14, Atomic Layer Epitaxy, pp. 601-663, Elsevier Science B. V. 1994, thedisclosure of which is incorporated herein by reference.

An extensive description of ALD precursors and ALD-grown materials hasbeen presented by Prof. M. Ritala and Prof. M. Leskelä in a recentreview article, Handbook of Thin Film Materials, Vol. 1: Deposition andProcessing of Thin Films, Chapter 2 “Atomic Layer Deposition”, pp.103-159, Academic Press 2002, incorporated by reference herein.

In context of the present application “a reaction space” designatesgenerally a reaction chamber, or a defined volume therein, in which theconditions can be adjusted so that deposition of a thin film ispossible.

In context of the present application, “an ALD type reactor” is areactor where the reaction space is in fluid communication with aninactive gas source and at least one, preferably at least two precursorsources such that the precursors can be pulsed into the reaction space.The reaction space is also preferably in fluid communication with avacuum generator (e.g. a vacuum pump), and the temperature and pressureof the reaction space and the flow rates of gases can be adjusted to arange that makes it possible to grow thin films by ALD type processes.

As is well known in the art, there are a number of variations of thebasic ALD method, including PEALD (plasma enhanced ALD) in which plasmais used for activating reactants. Conventional ALD or thermal ALD refersto an ALD method where

is not used but where the substrate temperature is high enough forovercoming the

barrier (activation energy) during collisions between the chemisorbedspecies on the surface and reactant molecules in the gas phase so thatup to a molecular layer of thin film grows on the substrate surfaceduring each ALD pulsing sequence or cycle. For the purpose

present invention, the term “ALD” covers both PEALD and thermal ALD.

“Metal source material” and “metal precursor” are used interchangeablyto designate a volatile or gaseous metal compound that can be used in anALD process. Preferred metal source materials and metal precursors canbe used as a starting compound for the corresponding metal oxide.

The term “multicomponent oxide” covers oxide materials comprising atleast two different metal cations.

According to preferred embodiments, titanium oxide containing thin filmsare deposited by ALD using titanium alkoxide precursors, more preferablythe specific alkoxide precursor Ti(OMe)₄.

In a preferred ALD type process, a gas phase pulse of an evaporatedtitanium alkoxide compound, preferably an evaporated titanium methoxidecompound, is introduced into the reaction space of an ALD reactor, whereit is contacted with a suitable substrate. No more than a monolayer ofthe titanium alkoxide compound adsorbs to the substrate surface in aself-limiting manner. Excess titanium alkoxide compound is removed fromthe reaction space by purging and/or evacuating the chamber.

Subsequently, a gas phase pulse of an oxygen source material isintroduced into the reaction space, where it reacts with the adsorbedtitanium precursor in a self-limiting manner. The oxygen source materialis preferably selected from the group consisting of water, oxygen,hydrogen peroxide, aqueous solution of hydrogen peroxide,

oxides of nitrogen, halide-oxygen compounds, peracids (—O—O—H),alcohols, alkoxides, oxygen-containing radicals and mixtures thereof. Inpreferred embodiments, ozone is used as the oxygen source material,since it does not form hydroxides with the alkaline earth materials.

By alternating the provision of the titanium precursor and the oxygen

material, a titanium oxide thin film can be deposited. A growth rate ofabout 0:10 to 0.20 Å/cycle is typically achieved in ALD processes.However, when TiO₂ was grown from titanium methoxide and ozone a growthrate of 0.55 Å/c was achieved at 250° C.

Optionally, an inactive gas can be used as a carrier gas duringdeposition. Inactive gas may also be used to purge the reaction chamberof excess reactant and reaction by-products, if any, between reactantpulses.

The deposition can be carried out at normal pressure, but it ispreferred to operate the process at reduced pressure. Thus, the pressurein the reactor is typically 0.01-20 mbar, preferably 0.1-5 mbar.

The reaction temperature can be varied depending on the evaporationtemperature and the decomposition temperature of the precursor. In someembodiments the range is from about 100 to 400° C., in particular about180 to 380° C. The substrate temperature is preferably low enough tokeep the bonds between thin film atoms intact and to prevent thermaldecomposition of the gaseous reactants. On the other hand, the substratetemperature is preferably high enough to keep the source materials ingaseous phase and avoid condensation. Further, the temperature ispreferably sufficiently high to provide the activation energy for thesurface reaction. In preferred embodiments the deposition temperature ispreferably between about 100 and about 300° C. It is particularlypreferred to grow titanium oxide films from titanium methoxide attemperatures of about 100-300° C., more preferably at about 250° C.

The titanium source temperature is preferably about 120 to 170° C., morepreferably about 140° C. In preferred embodiments, the reactiontemperature is somewhat higher than the titanium source temperature,typically about 20 to 160° C. higher. In the examples described below,maximum relative growth rates were obtained at 250 and 300° C. usingtitanium methoxide. The best values for the uniformity were alsoachieved at these temperatures. When the deposition temperature wasincreased from 160° C. to 250° C. the growth rate increases from 0.1 to0.55 Å/cycle (see FIG. 2). From a temperature of 250° C. to 300° C. thegrowth rate stayed at a relatively constant level of about 0.55 to 0.6Å/cycle. At 160° C. the non-uniformity was about 10%. This reactiontemperature is already relatively close to the evaporation temperatureof the Ti precursor. At a higher temperature the uniformity reacheslower values, i.e. about 1.5-0.6%.

For further details on the operation of a typical ALD process, referenceis made to the documents cited above.

The substrate can be of various types. Examples include, withoutlimitation, silicon, silica, coated silicon, germanium,silicon-germanium alloys, copper metal, noble and platinum metals groupincluding silver, gold, platinum, palladium, rhodium, iridium andruthenium, nitrides, such as transition metal nitrides, e.g. tantalumnitride TaN, carbides, such as transition metal carbides, e.g. tungstencarbide WC, and nitride carbides, e.g. tungsten nitride carbideWN_(x)C_(y). The preceding thin film layer deposited on the substrate,if any, will form the substrate surface for the next thin film.

In order to produce multicomponent oxide films, a second metal sourcematerial can be introduced to the ALD process. Additional metal sourcematerials can also be used, depending on the number of metals desired inthe thin film. For example, in some embodiments, a third, fourth, fifthetc. . . . metal compound is used. In some preferred embodiments, eachadditional metal source material is provided in a separate cycle, witheach cycle comprising feeding a vapor phase pulse of a metal sourcematerial, removing excess metal source material, providing a vapor phasepulse of an oxygen source material and removing excess oxygen sourcematerial. The same oxygen source material may be provided after eachmetal reactant, or different oxidants may be used to oxidize thedifferent metals. The number of cycles for each metal precursor may beapproximately equivalent or may be different, depending on thecomposition of the film that is desired.

In other embodiments, a pulse of the second metal source reactant is thenext reactant provided after the titanium source material in the samedeposition cycle. An oxidant is then provided to convert the two metalsto oxides. Additional metal reactants may also be provided prior toprovision of the oxygen containing source material. In otherembodiments, an oxidant is provided after each metal source reactant, asdiscussed above.

In addition, in some embodiments, the second (or additional) metalcompound is provided in each ALD cycle. That is, a pulse of the secondmetal compound is provided for each pulse of the titanium reactant.However, in other embodiments the second metal reactant is providedintermittently in the deposition process. In still other embodiments, ananolaminate structure is deposited by repeating a first cyclecomprising provision of the titanium precursor and and a first oxidantto deposit a thin film of titanium oxide, followed by repeating a secondcycle comprising provision of the second metal precursor to deposit athin film of the second metal oxide. The nanolaminate can start and endwith either metal, and the thickness of each layer can be determined bythe skilled artisan based on the particular circumstances.

Additional metal precursors can be metal compounds comprising a singlemetal or complex metal compounds comprising two or more metals. Themetal compounds are preferably selected from the group of volatile orgaseous compounds of transition metals and main group metals, i.e.,elements of groups 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 and/or 14(according to the system recommended by IUPAC) in the periodic table ofelements.

Since the properties of the metal compounds vary, the suitability ofeach metal compound for use in the ALD processes disclosed herein has tobe considered. The properties of the compounds can be found, e.g., in N.N. Greenwood and A. Earnshaw, Chemistry of the Elements, 1^(st) edition,Pergamon Press, 1986. The suitability of any particular compound canreadily be determined by a skilled artisan.

In some embodiments, preferred second metal source materials arehalides, preferably fluorides, chlorides, bromides or iodides, or metalorganic compounds, preferably alkoxy, alkylamino, cyclopentadienyl,dithiocarbamate or betadiketonate compounds of the desired metal(s).Also double metal precursors, i.e. molecules containing two metals in adiscrete ratio, may be used. In particular embodiments, cyclopentadienylbarium and/or cyclopentadienyl strontium compounds are used.

In some embodiments, barium, strontium, lanthanum and zirconium are usedas sources of a second and/or third and/or fourth etc. . . . metal internary and other multicomponent oxides. As mentioned above, the secondmetal source material (and any additional metal reactants) can beoxidized using the same or another oxygen source material as for thetitanium precursor.

In a particular embodiment a multicomponent oxide thin film comprisesbarium, strontium and titanium. The multicomponent oxide film may beBST. The multicomponent oxide is preferably deposited by alternatingthree deposition cycles, as described above. Thus, in one depositioncycle a vapour phase reactant pulse comprising a titanium compound,preferably a titanium alkoxide compound and more preferably a titaniummethoxide compound, is fed into the reaction chamber. Excess titaniumcompound and reaction by products, if any, are removed from the reactionchamber, preferably with the aid of an inert gas. An oxygen sourcematerial, preferably ozone, is then provided to the reaction chamberwhere it reacts with the chemisorbed titanium compound. In the secondcycle a barium compound, preferably a cyclopentadienyl compound, isprovided in the reactant pulse. In the third cycle a strontium compound,preferably a cyclopentadienyl strontium compound, is provided in thefirst reactant pulse. The three cycles may be provided in any order andthe deposition may begin and end with any of the cycles. In addition,one ratio of the cycles may be varied to provide the desiredcomposition, as can be determined by the skilled artisan.

In theory, a stoichiometric oxide ABO₃ can be obtained simply by pulsingthe two metal precursors and corresponding oxygen sources alternatelyand the growth rate of the ternary oxide can be predicted by summing thegrowth rates of the constituent oxides. In practice, however, bothassumptions often fail due to the different reactivities of theprecursors. The effect of surface chemistry usually causes changes inrelative growth rate, which can be determined by comparing the observedfilm thickness with the theoretical thickness calculated from the growthrates of binary oxides.

The novel thin film oxide deposition processes will find extensiveapplication as semiconductors, insulators and ferroelectrics. Inaddition, other applications will be apparent to the skilled artisan.

The following non-limiting example illustrates one embodiment of theinvention.

EXAMPLE 1

Four different titanium alkoxides were tested as metal precursors in ALDreactions to deposit TiO₂ using H₂O and O₃ as oxygen sources. Films weredeposited at temperatures of 100-300° C. (see FIGS. 1 a-g).

Reactions Using H₂O as the Oxygen Source Material:

a) TiO₂ films were deposited at 200-300° C. by ALD using alternatepulses of Ti(OEt)₄ as the titanium precursor and water as the oxidant.The growth rate increased from 0.30 to 0.39 Å/cycle with increasingtemperature. The film uniformity (Uf % 1σ) varied between 0.98 and 4.43,with the best uniformity being obtained at a deposition temperature of250° C.

b) TiO₂ films were deposited by ALD at deposition temperatures of200-300° C., using alternating pulses of Ti(O^(i)Pr)₄ as the titaniumprecursor and water as the oxidant. Growth rates were about 0.22-0.42Å/cycle, with the lowest value being obtained at 250° C. and the highestat 300° C. Film uniformity (Uf % 1σ) at these temperatures was 4.84 and6.84 respectively. For an unknown reason the film deposited at 200° C.was very non-uniform, having a uniformity of 23.53%.

c) TiO₂ films were deposited by ALD at deposition temperatures of 200,250 and 300° C., using alternating pulses of Ti(OBu)₄ as the titaniumprecursor and water as the oxidant. The growth rates at thesetemperatures were 0.26, 0.24 and 0.36 Å/cycle respectively. The mostuniform films were obtained at 250° C. (Uf % 1σ 0.81), while the Uf %were 3.33 and 1.73 at 200° C. and at 300° C. respectively.

d) For comparison, films were also deposited by ALD using Ti(OMe)₄ asthe titanium source material. The growth rates, in this case, increasedfrom 0.44 to 0.55 Å/cycle with increasing temperature (200-300° C.). Atthe same time the uniformity Uf % 1σ decreased from 2.26 to 0.80.

Reactions Using O₃ as the Oxygen Source Material:

a) TiO₂ films were deposited by ALD at 150-300° C., using alternatingpulses of Ti(OEt)₄ and O₃. The growth rate increased from 0.12 to 0.46Å/cycle with increasing temperature. At the same time, the filmuniformity (Uf % 1σ) decreased from 5.21 to 1.33, with the highestuniformity being obtained at 250° C.

b) TiO₂ films were deposited by ALD at 100-300° C., using alternatingpulses of Ti(O^(i)Pr)₄ and O₃. The growth rate was 0.08-0.58 Å/cycle,the lowest value being obtained at 100° C. and the highest value at 300°C. The film uniformity (Uf % 1σ) varied between 1.51 and 14.43, with thehighest uniformity being obtained at 200° C. and the lowest at 100° C.

c) TiO₂ films were deposited by ALD at 150-300° C., using alternatingpulses of Ti(OBu)₄ and O₃. The growth rate at these temperatures was0.26-0.99 Å/cycle. The best growth rate was obtained at 150° C. Thelowest growth rate was therefore 0.26 Å/cycle, obtained at 200° C., andthe highest growth rate was 0.39 Å/cycle, obtained at 300° C. The Uf %1σ decreased with increasing temperature (200-300° C.) from 3.80 to1.16, the value obtained at 150° C. being 10.30.

d) For comparison, the growth rate when using Ti(OMe)₄ increased withincreasing temperature (160-300° C.) from 0.11 to 0.61 Å/cycle. At thesame time the Uf % 1σ decreased from 10.43 to 0.65.

It will be appreciated by those skilled in the art that variousomissions, additions and modifications may be made to the processesdescribed above without departing from the scope of the invention, andall such modifications and changes are intended to fall within the scopeof the invention, as defined by the appended claims.

1. An atomic layer deposition process for producing titanium containingoxide thin films comprising alternately contacting a substrate in areaction space with vapor phase pulses of a titanium alkoxide and atleast one oxygen source material.
 2. The process according to claim 1,wherein the oxygen source material is selected from the group of water,oxygen, hydrogen peroxide, aqueous solution of hydrogen peroxide, ozone,oxides of nitrogen, halide-oxygen compounds, peracids (—O—O—H),alcohols, alkoxides, oxygen-containing radicals and mixtures thereof. 3.The process according to claim 2, wherein the oxygen source material isozone.
 4. The process according to claim 1, wherein the titaniumalkoxide source temperature is about 140° C.
 5. The process according toclaim 1, wherein the deposition temperature is in from about 100° C. toabout 300° C.
 6. The process according to claim 5, wherein thedeposition temperature is about 250° C.
 7. The process according toclaim 1, additionally comprising contacting the substrate withalternating pulses of a second metal precursor.
 8. The process accordingto claim 7, wherein the titanium containing oxide thin film is amulticomponent film.
 9. The process according to claim 7, wherein thesecond metal precursor is a metal compound comprising a single metal ora complex metal compound comprising two or more metals.
 10. The processaccording to claim 9, wherein the metal compound or the complex metalcompound comprises titanium, lanthanum or zirconium.
 11. A atomic layerdeposition type process for depositing a multicomponent oxide thin filmcomprising titanium, the process comprising contacting a substrate withalternate and sequential vapor phase pulses of a metal precursor and anoxygen source material, wherein the metal precursor is a titaniumalkoxide compound and the oxygen source material is ozone.
 12. Theprocess of claim 11, additionally comprising contacting the substratewith a vapor phase pulse of a second metal precursor.
 13. The process ofclaim 11, wherein the titanium alkoxide compound is a titanium methoxidecompound.
 14. The process of claim 11, wherein the multicomponent oxidecomprises barium and strontium.
 15. A method for growing a thin filmcomprising barium, strontium and titanium on a substrate in a reactionchamber by atomic layer deposition, wherein a first growth cyclecomprises: feeding a first reactant pulse into the reaction chamber,wherein the first reactant is a titanium methoxide compound; removingthe first reactant from the reaction chamber with the aid of an inertgas; feeding an oxygen source material into the reaction space, whereinthe second reactant is ozone; and removing excess second reactant fromthe reaction chamber with the aid of an inert gas.
 16. The method ofclaim 15, additionally comprising a second growth cycle, the secondgrowth cycle comprising: feeding a second reactant pulse into thereaction chamber, wherein the third reactant pulse is a barium compound;and removing excess second reactant from the reaction chamber with theaid of an inert gas; feeding an oxygen source material into the reactionchamber; and removing excess oxygen source material from the reactionchamber with the aid of an inert gas.
 17. The method of claim 16,wherein the oxygen source material is ozone.
 18. The method of claim 16,wherein the barium compound is a cyclopentadienyl compound.
 19. Themethod of claim 16, additionally comprising a third growth cycle, thethird growth cycle comprising: feeding a third reactant pulse into thereaction chamber, wherein the third reactant pulse is a strontiumcompound; and removing excess third reactant from the reaction chamberwith the aid of an inert gas; feeding an oxygen source material into thereaction chamber; and removing excess oxygen source material from thereaction chamber with the aid of an inert gas.
 20. The method of claim18, wherein the oxygen source material is ozone.
 21. The method of claim18, wherein the strontium compound is a cyclopentadienyl compound.